Oracle LAG Function

/* Formatted on 4:51:00 (QP5 v5.149.1003.31008 )*/
SELECT *
FROM (SELECT
A. lot_id,
A. shift_start_timekey,
A. event_name,
A. old_oper_code,
A. oper_code,
'-',
LAG (old_oper_code, 2) OVER (order by lot_id, event_timekey)
Previus_2,
LAG (old_oper_code, 1) OVER (order by lot_id, event_timekey)
Previus_1,
A. old_oper_code previus_0
FROM eds_lot_hist
WHERE a. factory = 'module' -- AND OLD_OPER_CODE = 'r510'
-- AND a. lot_id = '8awx1z0277b1c6'
AND shift_start_timekey = '2017 20120101'
AND a. old_oper_code <> a. oper_code
AND a. event_name IN ('trackout', 'trackoutrework', 'fa ')
Order by lot_id, event_timekey)
WHERE previus_2 IN ('r540', 'r530', 'r550 ', 'r510 ')
AND PREVIOUS_1 = 'r551'
AND PREVIOUS_0 = 'r510 ';